Method of Preparing a Dough-Based Product

ABSTRACT

Dough with a high sucrose content (such as cake dough) tends to inhibit the activity of an anti-staling amylase such as Novamyl, making it less effective to prevent the staling of dough-based products with high sucrose content such as cakes. A good anti-staling effect in cakes can be achieved by using a carefully selected anti-staling amylase with certain properties. Analysis of a 3D structure of Novamyl shows that sucrose may inhibit by binding in the active site. Sucrose docks into the active site of Novamyl differently from the substrate or inhibitor in published models 1QHO and 1QHP. This finding is used to design sucrose-tolerant variants.

SEQUENCE LISTING AND DEPOSITED MICROORGANISMS

Sequence Listing

The present invention comprises a sequence listing.

Deposit of Biological Material

None.

FIELD OF THE INVENTION

The present invention relates to the use of anti-staling amylases in the preparation of dough or dough-based edible products with a high sucrose content.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 3,026,205 describes a process of producing baked confections and the products resulting therefrom by alpha-amylase.

WO 9104669 describes the use of a maltogenic alpha-amylase to retard the staling of baked products such as bread; the maltogenic alpha-amylase described therein is commercially available under the tradename Novamyl® (product of Novozymes A/S). U.S. Pat. No. 6,162,628 describes Novamyl variants and their use for the same purpose. Three-dimensional structures of Novamyl are published in U.S. Pat. No. 6,162,628 and in the Protein Data Bank (available at http://www.rcsb.org/pdb/) with identifiers 1QHO and 1QHP.

SUMMARY OF THE INVENTION

The inventors have found that a high sucrose content dough (such as cake dough) tends to inhibit the activity of an anti-staling amylases such as Novamyl, making it less effective to prevent the staling of dough-based products with high sucrose content such as cakes. They have found that a good anti-staling effect in cakes can be achieved by using a carefully selected anti-staling amylase with certain properties, and they have identified such amylases.

By analyzing a 3D structure of Novamyl, the inventors further found that sucrose may inhibit by binding in the active site. They have found that sucrose docks into the active site of Novamyl differently from the substrate or inhibitor in published models 1QHO and 1QHP, and they have used this finding to design sucrose-tolerant variants.

Accordingly, the invention provides a method of preparing dough or a dough-based edible product (e.g. a baked product) by adding a sucrose-tolerant anti-staling amylase. It also provides novel sucrose tolerant variants of a maltogenic alpha-amylase.

DETAILED DESCRIPTION OF THE INVENTION

Maltogenic Alpha-Amylase and Sucrose Docking

A maltogenic alpha-amylase (EC 3.2.1.133) having more than 70% identity (particularly more than 80% or 90%, such as at least 95% or 96% or 97% or 98% or 99%) with the Novamyl sequence shown as SEQ ID NO: 1 may be used as the parent enzyme for designing sucrose tolerant variants. Amino acid identity may be calculated as described in U.S. Pat. No. 6,162,628.

For Novamyl (SEQ ID NO: 1), a 3D structure including a substrate or inhibitor as described in U.S. Pat. No. 6,162,628 or in the Protein Data Bank with the identifier 1QHO or 1QHP may be used. Alternatively, a Novamyl variant may be used, such as a variant described in U.S. Pat. No. 6,162,628 or in this specification, e.g. the variant F188L+D261G+T288P. A 3D structure of a variant may be developed from the Novamyl structure by known methods, e.g. as described in T. L. Blundell et al., Nature, vol. 326, p. 347 ff (26 Mar. 1987); J. Greer, Proteins: Structure, Function and Genetics, 7:317-334 (1990); or Example 1 of WO 9623874.

The inventors found that sucrose may inhibit Novamyl by binding in the active site. Docking of sucrose into the active site of Novamyl (using the software GOLD version 2.1.2, Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK and the protein part of the x-ray structure 1QHO.pdb) reveals a specific binding configuration as unique to sucrose. The cartesian coordinates for the sucrose atoms in this binding configuration, using the coordinate system of the x-ray structure 1QHO.pdb are given in FIG. 1.

Maltogenic Alpha-Amylase Assay

The activity of a maltogenic alpha-amylase may be determined using an activity assay such as the MANU method. One MANU (Maltogenic Amylase Novo Unit) is defined as the amount of enzyme required to release one micro-mole of maltose per minute at a concentration of 10 mg of maltotriose substrate per ml in 0.1 M citrate buffer at pH 5.0, 37° C. for 30 minutes.

Amino Acid Alterations

The amino acid sequence of a maltogenic alpha-amylase may be altered to decrease the sucrose inhibition. The inventors found that the alteration may be made at an amino acid residue having at least one atom within 4 Ångstroms from any of the sucrose atoms when the sucrose molecule is docked in the 3D structure of the maltogenic alpha-amylase. Using the Novamyl structure 1QHO and the sucrose docking in FIG. 1, the following Novamyl residues are within 4 Å: K44, N86, Y89, H90, Y92, W93, F188, T189, D190, P191, A192, F194, D372, P373, R376.

Further the following positions have been identified as relevant: I15, R81, T87, G88, L196, N371 or N375 of SEQ ID NO: 1.

The alteration may be a substitution or deletion of one or more of the selected residues, or one or more residues (particularly 1-4 residues or 5-6 residues) can be inserted adjacent to a selected residue.

The substitution may be with a smaller or larger residue. A substitution to increase the size of the residue may diminish the space obtained by the docked sucrose molecule thereby preventing the binding of sucrose. Amino acid residues are ranked as follows from smallest to largest: (an equal sign indicates residues with sizes that are practically indistinguishable): G<A=S=C<V=T<P<L=I=N=D=M<E=Q<K<H<R<F<Y<W

The substitution may also be such as to eliminate contacts with the sucrose molecule, in particular by moving or removing potential sites of hydrogen bonding or Van der Waals interactions.

The substitution may particularly be with another residue of the same type where the type is negative, positive, hydrophobic or hydrophilic. The negative residues are D,E, the positive residues are K/R, the hydrophobic residues are A, C, F, G, I, L, M, P, V, W, Y, and the hydrophilic residues are H, N, Q, S, T.

Some particular examples of substitutions are I15T/S/V/L, R18K, K44R/S/T/Q/N, N86Q/S/T, T87N/Q/S, G88A/S/T, Y89W/F/H, H90W/F/Y/R/K/N/Q/M, W93Y/F/M/E/G/V/T/S, F188H/L/I/T/G/V, D190E/Q/G, A192S/T, F194S/L/Y, L196F, N371K/R/F/Y/Q, D372E/Q/S/T/A and N375S/T/D/E/Q.

Examples of deletions are deletion of residue 191 or 192. An example of an insertion is Ala inserted between 192 and 193.

The polypeptide may include other alterations compared to Novamyl (SEQ ID NO: 1), e.g. alterations to increase the thermostability as described in U.S. Pat. No. 6,162,628.

Nomenclature for Amino Acid Alterations

In this specification, an amino acid substitution is described by use of one-letter codes, e.g. K44R. Slashes are used to indicate alternatives, e.g. K44R/S/T/Q/N to indicate substitution of K44 with R or S etc. P191* indicates a deletion of P191. *192aA indicates insertion of one Ala after A192. Commas are used to indicate multiple alterations in the sequence, e.g. F188L, D261G, T288P to indicate a variant with three substitutions.

Properties of Anti-Staling Amylase for Use with Sucrose

The amylase for use in high-sucrose dough may be selected so as to have mainly exo-amylase activity. More specifically, the amylase hydrolyzes amylose so that the average molecular weight of the amylose after 0.4-4% hydrolysis is more than 50% (particularly more than 75%) of the molecular weight before the hydrolysis.

Thus, the amylase may hydrolyze amylose (e.g. wheat amylose or synthetic amylose) so that the average molecular weight of the amylose after 0.4-4% hydrolysis (i.e. between 0.4-4% hydrolysis of the total number of bonds) is more than 50% (particularly more than 75%) of the value before the hydrolysis. The hydrolysis can be conducted in a 1.7% amylose solution by weight at suitable conditions (e.g. 10 minutes at 60° C., pH 5.5), and the molecular weight distribution before and after the hydrolysis can be determined by HPLC. The test may be carried out as described in C. Christophersen et al., Starch 50 (1), 39-45 (1998).

An exo-amylase for use in high-sucrose dough may have a specified sugar tolerance. Compared to its activity in the absence of sucrose, the amylase may have more than 20% activity at 10% sugar, more than 10% activity at 20% sucrose, or more than 4% activity at 40% sucrose. The sugar tolerance may be determined as described in the examples.

The exo-amylase may have optimum activity in the pH range 4.5-8.5. It may have sufficient thermostability to retain at least 20% (particularly at least 40%) activity after 30 minutes incubation at 85° C. at pH 5.7 (50 mM Na-acetate, 1 mM CaCl₂) without substrate.

The exo-amylase may be added to the dough in an amount corresponding to 1-100 mg enzyme protein per kg of flour, particularly 5-50 mg per kg.

The exo-amylase may be non-liquefying. This can be determined by letting the exo-amylase act on a 1% wheat starch solution until the reaction is complete, i.e. addition of fresh enzyme causes no further degradation, and analyzing the reaction products, e.g. by HPLC. Typical reaction conditions are e.g. 0.01 mg enzyme per ml starch solution for 48 hours. The exo-amylase is considered non-liquefying if the amount of residual starch after the reaction is at least 20% of the initial amount of starch.

The exo-amylase may have maltogenic alpha-amylase activity (EC 3.2.1.133). The exo-amylase may be the amylase described in DK PA 2004 00021, or it may be a Novamyl variant described in this specification.

Dough and Dough-Based Edible Product

The dough may have a sucrose content above 10% by weight, particularly above 20% or 30%, e.g. 30-40%. The flour content is typically 25-35% by weight of total ingredients. The dough may be made by a conventional cake recipe, typically with cake flour, sugar, fat/oil and eggs as the major ingredients. It may include other conventional ingredients such as emulsifiers, humectants, gums, starch and baking powder. It generally contains such ingredients as soft wheat flour, milk or other liquids, sugar, eggs, chemical leaveners, flavor extracts and spices, as well as others that may or may not include shortening.

The dough is generally heat treated, e.g. by baking or deep frying to prepare an edible product such as cakes including pound cake, yellow and white layer cakes, cakes containing chocolate and cocoa products, sponge cakes, angel food cake, fruit cakes and foam-type cakes and doughnuts.

EXAMPLES Example 1 Sucrose Tolerance of Novamyl Variants

The amylase activity of a number of polypeptides were tested by incubation with Phadebas tablets (product of Pharmacia®) for 15 minutes at 60° C. in the presence of sucrose at various concentrations (in % by weight). The results are expressed in % of the result without sugar: Alterations compared to 0% 10% 20% 40% SEQ ID NO: 1 sucrose sucrose sucrose sucrose None 100 13 6 1.5 F188L, D261G, T288P 100 27.5 14.5 6 F194S 100 31.5 18.5 7.5 L196F 100 69 42 23 D190G 100 65 43 21

Example 2 Sucrose Tolerance of Novamyl Variants

A number of polypeptides were tested as in Example 1. The results are expressed as activity with 10% sucrose in % of the activity without sucrose: Alterations compared to Sugar SEQ ID NO: 1 tolerance None 15 D261G, T288P 24 F188L, D261G, T288P 35 T288P 56 Y89F, D261G, T288P 42 N86V, F188L, D261G, T288P 37 Y89F, F188L, D261G, T288P 38 Y89H, F188L, D261G, T288P 50 N86T, F188L, D261G, T288P 49 F194S, D261G, T288P 47 L196F 65 D261G, T288P, D372V 62 Q184H, N187D, F194Y 47 D190G 66 N86G, Y89M, F188L, D261G, T288P 47 F188L, D190G, D261G, T288P 68 A192Q, D261G, T288P, S446A 46 F188H 49 P191* 42 A192* 51 A192*, G193* 67 *192aA 44 N86K, F252L, D261G, T288P 49 F194Y, L225S, D261G, T288P 49 F194L, D261G, T288P 54 F194S, D261G, T288P, P642Q 60 D261G, T288P, N375S 58 F188T 37 F188G 36 F188V 41 A192R, F194L, D261G, T288P, G469R 60 A192G, D261G, T288P 41 Y89F, D261G, T288P, I290V, N375S 60

The following variants are also considered of interest in the context of the present invention: Alterations compared to SEQ ID NO: 1 115T, N86K, P191S, D261G, T288P I15T, P191S, D261G, T288P I15T, P191S, Y258F, D261G, T288P, N375S, Y549C, Q648H I15T, G153R, P191S, D261G, T288P, N371K, K645R

Example 3 Sucrose Tolerance and Thermostability of Amylases

The following amylases were tested for thermostability and sugar tolerance: bacterial alpha-amylase from B. amyloliquefaciens (BAN™, product of Novozymes A/S), fungal alpha-amylase from A. oryzae (Fungamyl®, product of Novozymes A/S), maltogenic alpha-amylase having the sequence of SEQ ID NO: 1 (Novamyl®, product of Novozymes A/S), a Novamyl variant having SEQ ID NO: 1 with the substitutions F188L+D261G+T288P, and bacterial alpha-amylase from B. licheniformis (Termamyl®, product of Novozymes A/S).

Exo-Amylase Activity

The five amylases were tested for exo-amylase activity as described above. The results show that Novamyl and the Novamyl variant had exo-amylase activity by this test, and the other three did not.

Thermostability

Each amylase was incubated at 85° C. at pH 5.7 (50 mM Na-acetate, 1 mM CaCl₂) without substrate, and the amylase activity was measured after 0, 15, 30 and 60 minutes heat treatment. The results are expressed as residual activity in % of the initial activity: 0 15 30 60 BAN 100 3 1 0 Fungamyl 100 0 0 0 Novamyl 100 51 29 13 Novamyl variant 100 64 48 54 Termamyl 100 100 71 85

The results show that the Novamyl variant and Termamyl were not deactivated by the heat-treatment. BAN and Fungamyl lose all their activity after 15 min while Novamyl loses it gradually with heat-treatment time.

Sucrose Tolerance

The experiment was repeated in 10% sucrose solution. The results are expressed as residual activity in % of the initial activity without sucrose: 0 15 30 60 BAN 93 2 1 0 Fungamyl 31 0 0 0 Novamyl 7 6 1 3 Novamyl variant 21 19 14 16 Termamyl 116 112 97 82

The results show that BAN and Termamyl were not inhibited by sugar while Fungamyl and the Novamyl variant were somewhat inhibited, and Novamyl was heavily inhibited by sugar. The combination of sugar and heat-treatment shows that the Novamyl variant and Termamyl could be active during baking of cakes. Termamyl and the Novamyl variant fulfill the criterion for thermostability and sugar tolerance used in this invention.

Example 4 Preparation of Sponge Cake with Amylase

Sponge cakes were made with addition of amylase as follows: BAN (0.83. 8.3 or 83 mg/kg flour), Novamyl (1.3 or 13 mg/kg flour) or the Novamyl variant used in Example 1 (1, 10 or 100 mg/kg flour). A control cake was made without amylase.

The cakes were baked according to the High Ratio Sponge Sandwich Cake (HRSSC) method. After baking, the cakes were cooled down for 60-120 minutes, and the cakes were stored at room temperature in sealed plastic bags filled with nitrogen until analysis. The cakes were evaluated on day 1, 3, 7 or 23.

Texture profile analysis (TPA) was performed as described in Bourne M. C. (2002) 2. ed., Food Texture and Viscosity: Concept and Measurement. Academic Press. The results showed that the increase in hardness was slower with increasing dosage of the Novamyl variant. The addition of BAN or Novamyl had only a slight effect, and only at the highest dosage.

The cohesiveness of the cakes decreased with storage time. The addition of the Novamyl variant delayed this decrease. The addition of BAN or Novamyl had a slight effect, and only at the highest dosage.

Water mobility was characterized by low field NMR. The addition of the Novamyl variant and BAN increased the mobility, indicating that the two amylases were able to keep the cakes more moist. Novamyl had virtually no effect.

A small sensory evaluation of softness and moistness was performed on day 13 for the 3 cakes with the Novamyl variant and the control cake. The cakes were evaluated regarding three parameters; Firmness, Moistness and preferability. The control was the firmest, driest and least preferred. The higher dosage of the Novamyl variant, the less firm (softer), moister and better liked.

A large panel sensory evaluation was performed on day 13. It was a paired comparison test where a control cake was compare to the cake with the Novamyl variant at the highest dosage. A 30-member panel was asked two questions (1) Which cake is moister and (2) which cake is fresher. All panel members agreed on that the cake with the Novamyl variant was moister and fresher. The preference was significant at a significance level above 99.999%.

To summarize, the data show that the Novamyl variant had anti-staling properties and was able to improve moistness perception and moistness measured by NMR. The two other amylases had only a slight effect.

Example 5 High-Ratio Unit Cakes

Cakes were made with addition of amylase as follows: BAN (0.83. 8.3 or 83 mg/kg flour) or the Novamyl variant used in Example 1 (1, 10 or 100 mg/kg flour). A control cake was made without amylase.

Cakes were baked according to the High ratio unit cake (HRUC) method. After baking, the cakes were cooled down for 60-120 minutes, and the cakes were stored at room temperature in sealed plastic bags filled with Nitrogen until analysis. The cakes were evaluated on day 7, 20 and 34 by the same methods as in the previous example.

The increase in hardness was slower with the Novamyl variant at the highest dosage. The addition of BAN to the cake resulted in a low volume and a doughy cake which gave poor results in hardness measurements.

The addition of the Novamyl variant delayed the decrease in cohesiveness while BAN did not influence it at all.

The Novamyl variant and BAN were able to keep the cake more moist than the control. This increase in mobility of the free water could partly be explained by the cakes with BAN and the Novamyl variant being able to retain the moisture content.

A small sensory evaluation on day 34 showed that the cake with the Novamyl variant at the highest dosage was clearly better than the control cake; it was more moist and it was less crumbly.

Over-all, there was an anti-staling effect of the Novamyl variant at the high dosage, similar to the effect on sponge cakes in the previous example. The staling of HRUC cakes was slower than Sponge cakes but it was still evident that the Novamyl variant had an anti-staling effect. The anti-staling effect was seen with texture analysis, NMR and sensory evaluation. BAN showed anti-staling effects in HRUC but it was sensitive to over-dosage which resulted in cake collapse and a doughy cake.

Example 6 Sponge Cake

Sponge cakes were made with addition of the amylase of DK PA 2004 00021 at dosages 0.5, 1, 2, 5 and 20 mg/kg flour and a control cake without amylase.

Texture and NMR was measured on day 1, 7 and 13. The addition of the amylase reduced the increase in firmness, especially at the highest dosage. The amylase also had a beneficial effect on the mobility of water which was correlated with the moistness of the cake.

A blind sensory ranking evaluation performed on day 14 showed a ranking according to the dosage, the higher dosage the more soft and moist cake. The most preferred cake was the one with the highest dosage.

Example 7 Baking Procedure Tegral Allegro Cake

Recipe

The following recipe was used: % Tegral Allegro mix* 100 Pasteurized whole egg 50 Butter 50 Enzymes According to trial. 0 or 25 mg/kg flour. *commercially available from Puratos NV/SA, Groot-Bijgaarden, Belgium Procedure

The ingredients were scaled into a mixing bowl and mixed using an industrial mixer (e.g. Bjørn AR 5 A Varimixer) with a suitable paddle speed. 300 g of the dough was poured into forms. The cakes are baked in a suitable oven (e.g. Sveba Dahlin deck oven) for 45 min. at 180° C. The cakes were allowed to cool down at room temperature for 1 hour.

The volume of the cakes was determined when the cakes had cooled down using the rape seed displacement method. The cakes were packed under nitrogen in sealed plastic bags and stored at room temperature until analysis.

The cakes were evaluated on day 1, 7 and 14, two cakes were used at each occasions.

The cohesiveness and hardness of the cakes was evaluated with Texture analyser and the water mobility was characterized by low field NMR.

The Texture profile analysis (TPA) was performed as described in Bourne M. C. (2002) 2. ed., Food Texture and Viscosity: Concept and Measurement. Academic Press.

The mobility of free water was determined as described by P. L. Chen, Z. Long, R. Ruan and T. P. Labuza, Nuclear Magnetic Resonance Studies of water Mobility in Bread during Storage. Lebensmittel Wissenschaft und Technologie 30, 178-183 (1997). The mobility of free water has been described in literature to correlate to moistness of bread crumb.

Result

Compared to cakes with no addition of enzymes the volume of the cakes is not affected by the addition of the reference enzyme (SEQ ID NO: 1) nor by the addition of variants hereof, i.e. the cakes did not collapse upon addition of enzyme.

The cohesiveness of the cakes decreased with storage time. The addition of variants of SEQ ID NO: 1 delayed this decrease as can be seen in Table 1. TABLE 1 Change in Cohesiveness [gs/gs] with storage time of cakes with 25 mg protein enzyme per kg flour Enzyme Day 1 Day 7 Day 14 No enzyme 0.44 0.35 0.32 Seq ID No: 1 0.43 0.38 0.36 F188L, D261G, T288P 0.46 0.42 0.41 Y89F, D261G, T288P 0.45 0.43 0.39 N86G, Y89M, F188L, D261G, T288P 0.44 0.42 0.38 T288P 0.44 0.40 0.41 F194S, D261G, T288P 0.47 0.43 0.42 D261G, T288P, D372V 0.46 0.43 0.37 A192Q, D261G, T288P, S446A 0.44 0.42 0.39 A192R, F194L, D261G, T288P, G469R 0.47 0.44 0.42 A192G, D261G, T288P 0.46 0.42 0.39 N86K, F252L, D261G, T288P 0.45 0.41 0.39 F194L, D261G, T288P 0.45 0.42 0.42 F194S, D261G, T288P, P642Q 0.44 0.40 0.39 Y89F, D261G, T288P, I290V, N375S 0.43 0.42 0.40

The free water mobility is correlated with the moist perception of the cake crumb, it decreases with time. The addition of the Novamyl variants increased the mobility compared to the control, indicating that the amylases were able to keep the cakes more moist. Results are listed in Table 2. TABLE 2 Change in free water mobility [micros] with storage time of cakes with 25 mg protein enzyme per kg flour Enzyme Day 1 Day 7 Day 14 No enzyme 7077 5111 4175 Seq ID No: 1 6990 5460 4583 F188L, D261G, T288P 7216 5624 4656 Y89F, D261G, T288P 7085 6044 5151 N86G, Y89M, F188L, D261G, T288P 7493 5349 5120 T288P 7458 5785 4858 F194S, D261G, T288P 7746 6373 5325 D261G, T288P, D372V 7417 5517 4525 A192Q, D261G, T288P, S446A 7357 5714 5041 A192R, F194L, D261G, T288P, G469R 7549 5536 no data A192G, D261G, T288P 7546 5815 no data N86K, F252L, D261G, T288P 7349 5295 4775 F194L, D261G, T288P 7773 6803 5750 F194S, D261G, T288P, P642Q 8152 5969 4971 Y89F, D261G, T288P, I290V, N375S 7753 6175 4811

The hardness of the cakes increased with storage time. The addition of variants of SEQ ID NO: 1 delayed this increase in hardness as can be seen in Table 3. TABLE 3 Change in hardness [g] with storage time of cakes with 25 mg protein enzyme per kg flour Enzyme Day 1 Day 7 Day 14 No enzyme 647 1060 1408 Seq ID No: 1 677 997 1171 F188L, D261G, T288P 683 951 1167 Y89F, D261G, T288P 649 998 1160 N86G, Y89M, F188L, D261G, T288P 630 844 1194 T288P 719 1101 1098 F194S, D261G, T288P 672 943 1061 D261G, T288P, D372V 593 962 1344 A192Q, D261G, T288P, S446A 680 931 1159 A192R, F194L, D261G, T288P, G469R 720 987 1209 A192G, D261G, T288P 707 1024 1102 N86K, F252L, D261G, T288P 678 955 1248 F194L, D261G, T288P 648 895 1050 F194S, D261G, T288P, P642Q 674 1028 1316 Y89F, D261G, T288P, I290V, N375S 602 731 827 

1. A method of preparing a dough or a dough-based edible product, comprising adding a polypeptide to the dough, wherein the dough comprises at least 10% sucrose by weight, and the polypeptide: a) has an amino acid sequence which is at least 70% identical to SEQ ID NO: 1, and b) compared to SEQ ID NO: 1 comprises an amino acid alteration which is substitution or deletion of or insertion adjacent to I15, R18, K44, N86, T87, G88, Y89, H90, Y92, W93, F188, T189, D190, P191, A192, F194, L196, D329, N371, D372, P373, N375 or R376.
 2. The method of claim 1 wherein the alteration is substitution with a larger or smaller amino acid residue.
 3. The method of claim 1 wherein the alteration is insertion of 1-4 amino acid residues at the N- or C-side of the specified residue.
 4. The method of claim 1 wherein the polypeptide comprises a substitution I15T/S/V/L, R18K, K44R/S/T/Q/N, N86Q/S/T, T87N/Q/S, G88A/S/T, Y89W/F/H, H90W/F/Y/R/K/N/Q/M, W93Y/F/M/E/G/V/T/S, F188H/L/I/T/G/V, D190E/Q/G, A192G/S/T/Q/R, F194S/L/Y, L196F, N371K/R/F/Y/Q or D372E/Q/S/T/A, a deletion of 191 or 192 or an insertion of Ala after
 192. 5. The method of claim 1 wherein the polypeptide has the amino acid sequence of SEQ ID NO: 1 with one of the following sets of alterations: Alterations compared to SEQ ID NO: 1 D261G, T288P F188L, D261G, T288P T288P Y89F, D261G, T288P N86V, F188L, D261G, T288P Y89F, F188L, D261G, T288P Y89H, F188L, D261G, T288P N86T, F188L, D261G, T288P F194S, D261G, T288P L196F D261G, T288P, D372V Q184H, N187D, F194Y D190G N86G, Y89M, F188L, D261G, T288P F188L, D190G, D261G, T288P A192Q, D261G, T288P, S446A F188H P191* A192* A192*, G193* *192aA N86K, F252L, D261G, T288P F194Y, L225S, D261G, T288P F194L, D261G, T288P F194S, D261G, T288P, P642Q D261G, T288P, N375S F188T F188G F188V A192R, F194L, D261G, T288P, G469R A192G, D261G, T288P Y89F, D261G, T288P, I290V, N375S


6. A polypeptide which: a) has amylase activity which is less inhibited by sucrose than the amylase activity of SEQ ID NO: 1, b) has an amino acid sequence which is at least 70% identical to SEQ ID NO: 1, and c) compared to SEQ ID NO: 1 comprises an amino acid alteration which is substitution or deletion of or insertion adjacent to K44, Y89, H90, Y92, W93, D329, D372, P373 or R376 or an alteration N86T/VG/K, T87N/Q, H90W/F/Y/R/M, F188I/L/T/G/V, D190G, P191*, A192G/Q/R, F194S/L/Y, L196F, L225S, F252L, D261G, T288P, I290V, N371K/R/F/Y/Q, D372E/Q/S/T/A/V, N375S, S446A, G469R, S578G or P642Q.
 7. The polypeptide of claim 6 wherein the alteration is substitution with a larger or smaller amino acid residue.
 8. The polypeptide of claim 6 which comprises insertion of 1-4 amino acid residues at the N- or C-side of the specified residue.
 9. The polypeptide of claim 6 which comprises a substitution K44R/S/T/Q/N, Y89W/F/H, W93Y/F/M/E/G/V/T/S, D261G, T288P.
 10. The polypeptide of claim 6 which has the amino acid sequence of SEQ ID NO: 1 with one of the following sets of alterations: F194L, S578G N171S, S175C, F194L, V215D, Q449R L196F Y89F, D261G, T288P D261G, T288P Q184H, N187D, F194Y D190G Y89F, D261G, T288P A192*, G193* N86V, F188L, D261G, T288P Y89F, F188L, D261G, T288P Y89H, F188L, D261G, T288P N86T, F188L, D261G, T288P F194S, D261G, T288P D261G, T288P, D372V D190G N86G, Y89M, F188L, D261G, T288P F188L, D190G, D261G, T288P A192Q, D261G, T288P, S446A N86K, F252L, D261G, T288P F194Y, L225S, D261G, T288P F194L, D261G, T288P F194S, D261G, T288P, P642Q D261G, T288P, N375S A192R, F194L, D261G, T288P, G469R A192G, D261G, T288P Y89F, D261G, T288P, I290V, N375S F188T F188G F188V


11. A method of preparing a polypeptide, comprising a) providing a parent polypeptide having an amino acid sequence, and having maltogenic alpha-amylase activity, b) selecting an amino acid residue in the sequence corresponding to I15, R18, K44, N86, T87, G88, Y89, H90, Y92, W93, F188, T189, D190, P191, A192, F194, L196, D329, N371 D372, P373, N375 or R376 in SEQ ID NO: 1, c) substituting or deleting the selected residue or inserting one or more residues adjacent to the selected residue to obtain an altered amino acid sequence, d) preparing an altered polypeptide having the altered amino acid sequence, e) testing the amylase activity and the sugar tolerance of the altered polypeptide, and f) selecting a polypeptide which has amylase activity and has higher sucrose tolerance than the parent polypeptide.
 12. A method of constructing a polypeptide, comprising: a) providing a parent maltogenic alpha-amylase having an amino acid sequence and a three-dimensional structure, b) docking a sucrose molecule in the structure, c) selecting an amino acid residue having a C-alpha atom located <10 Å from an atom in the docked sucrose molecule, d) substituting or deleting the selected residue or inserting one or more residues adjacent to the selected residue to obtain an altered amino acid sequence, e) docking a sucrose molecule in a structure of the polypeptide having the altered sequence and calculating the binding energy for the sucrose, and f) selecting a polypeptide wherein the binding energy and/or binding configuration is changed.
 13. A method of preparing dough or a dough-based edible product, comprising adding an exo-amylase to dough wherein the dough comprises at least 10% sucrose by weight, and the exo-amylase has amylase activity in the presence of 10% sucrose by weight which is more than 20% of the activity without sucrose.
 14. The method of the preceding claim wherein the exo-amylase retains at least 20% (particularly at least 40%) activity after 30 minutes incubation at 85° C. at pH 5.7 (50 mM Na-acetate, 1 mM CaCl₂) without substrate. 